For variable magnetic flux motors and variable magnetic flux electric generators, a variable magnet and a stationary magnet are used. Conventionally, Al—Ni—Co based magnets and Fe—Cr—Co based magnets are used for the variable magnet. For example, the Al—Ni—Co based magnet has a coercive force of 150 kA/m or less. There are demands for a variable magnet having a coercive force of 200 to 500 kA/m in order to realize a more efficient variable magnetic flux motor or the like.
Sm—Co based magnets and Nd—Fe—B based magnets are known as high performance permanent magnets. Among the Sm—Co based magnets, a Sm2Co17 type magnet obtains a coercive force on the basis of a fine structure which is called a cell structure that has a 1-5 type crystal phase precipitated in a grain boundary of a 2-17 type crystal phase. The magnet domain wall of the Sm2Co17 type magnet has a thickness of about 2 to 10 nm, bur a conventional 1-5 type crystal phase (grain boundary phase) has a thickness of about several tens nm, so that the coercive force is increased by pinning of the magnetic domain wall. For example, the coercive force of the Sm2Co17 type magnet is 1430 kA/m at the maximum. Therefore, it cannot be used as a variable magnet.